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Joughin I, Shean DE, Smith BE, Floricioiu D. A Decade of Variability on Jakobshavn Isbrae: Ocean Temperatures Pace Speed Through Influence on Mélange Rigidity. THE CRYOSPHERE 2020; 14:211-227. [PMID: 32355554 PMCID: PMC7192015 DOI: 10.5194/tc-14-211-2020] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
The speed of Greenland's fastest glacier, Jakobshavn Isbrae, has varied substantially since its speedup in the late 1990s. Here we present observations of surface velocity, mélange rigidity, and surface elevation to examine its behaviour over the last decade. Consistent with earlier results, we find a pronounced cycle of summer speedup and thinning followed by winter slowdown and thickening. There were extended periods of rigid mélange in the winters of 2016-17 and 2017-18, concurrent with terminus advances ~6 km farther than in the several winters prior. These terminus advances to shallower depths caused slowdowns, leading to substantial thickening, as has been noted elsewhere. The extended periods of rigid mélange coincide well with a period of cooler waters in Disko Bay. Thus, along with the relative timing of the seasonal slowdown, our results suggest that the ocean's dominant influence on Jakobshavn Isbrae is through its effect on winter mélange rigidity, rather than summer submarine melting. The elevation time series also reveals that in summers when the area upstream of the terminus approaches flotation, large surface depressions can form, which eventually become the detachment points for major calving events. It appears that as elevations near flotation, basal crevasses can form, which initiates a necking process that forms the depressions. The elevation data also show that steep cliffs often evolve into short floating extensions, rather than collapsing catastrophically due to brittle failure. Finally, summer 2019 speeds were slightly faster than the prior two summers, leaving it unclear whether the slowdown is ending.
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Affiliation(s)
- Ian Joughin
- Applied Physics Laboratory, University of Washington, Seattle, 98105, USA
| | - David E. Shean
- Department of Civil and Environmental Engineering, University of Washington, Seattle, 98185, USA
| | - Benjamin E. Smith
- Applied Physics Laboratory, University of Washington, Seattle, 98105, USA
| | - Dana Floricioiu
- German Aerospace Center (DLR), Remote Sensing Technology Institute, SAR Signal Processing, Muenchenerstr. 20, 82230 Wessling, Germany
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An L, Rignot E, Mouginot J, Millan R. A Century of Stability of Avannarleq and Kujalleq Glaciers, West Greenland, Explained Using High-Resolution Airborne Gravity and Other Data. GEOPHYSICAL RESEARCH LETTERS 2018; 45:3156-3163. [PMID: 29937605 PMCID: PMC5993245 DOI: 10.1002/2018gl077204] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/27/2018] [Accepted: 02/09/2018] [Indexed: 06/08/2023]
Abstract
The evolution of Greenland glaciers in a warming climate depends on their depth below sea level, flow speed, surface melt, and ocean-induced undercutting at the calving front. We present an innovative mapping of bed topography in the frontal regions of Sermeq Avannarleq and Kujalleq, two major glaciers flowing into the ice-choked Torssukatak Fjord, central west Greenland. The mapping combines a mass conservation algorithm inland, multibeam echo sounding data in the fjord, and high-resolution airborne gravity data at the ice-ocean transition where other approaches have traditionally failed. We obtain a reliable, precision (±40 m) solution for bed topography across the ice-ocean boundary. The results reveal a 700 m deep fjord that abruptly ends on a 100-300 m deep sill along the calving fronts. The shallow sills explain the presence of stranded icebergs, the resilience of the glaciers to ocean-induced undercutting by warm Atlantic water, and their remarkable stability over the past century.
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Affiliation(s)
- L. An
- Department of Earth System ScienceUniversity of CaliforniaIrvineCAUSA
| | - E. Rignot
- Department of Earth System ScienceUniversity of CaliforniaIrvineCAUSA
- Jet Propulsion LaboratoryCalifornia Institute of TechnologyPasadenaCAUSA
| | - J. Mouginot
- Department of Earth System ScienceUniversity of CaliforniaIrvineCAUSA
| | - R. Millan
- Department of Earth System ScienceUniversity of CaliforniaIrvineCAUSA
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Elevation Change and Improved Velocity Retrieval Using Orthorectified Optical Satellite Data from Different Orbits. REMOTE SENSING 2017. [DOI: 10.3390/rs9030300] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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Holland DM, Voytenko D, Christianson K, Dixon TH, Mei MJ, Parizek BR, Vaňková I, Walker RT, Walter JI, Nicholls K, Holland D. An Intensive Observation of Calving at Helheim Glacier, East Greenland. OCEANOGRAPHY (WASHINGTON, D.C.) 2016; 29:46-61. [PMID: 32818012 PMCID: PMC7430530 DOI: 10.5670/oceanog.2016.98] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Calving of glacial ice into the ocean from the Greenland Ice Sheet is an important component of global sea level rise. The calving process itself is relatively poorly observed, understood, and modeled; as such, it represents a bottleneck in improving future global sea level estimates in climate models. We organized a pilot project to observe the calving process at Helheim Glacier in East Greenland in an effort to better understand it. During an intensive one-week survey, we deployed a suite of instrumentation including a terrestrial radar interferometer, GPS receivers, seismometers, tsunameters, and an automated weather station. This effort captured a calving process and measured various glaciological, oceanographic, and atmospheric parameters before, during, and after the event. One outcome of our observations is evidence that the calving process actually consists of a number of discrete events, spread out over time, in this instance over at least two days. This time span has implications for models of the process. Realistic projections of future global sea level will depend on accurate parametrization of calving, which will require more sustained observations.
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Affiliation(s)
- David M Holland
- Courant Institute of Mathematical Sciences, New York University, New York, NY, USA, and Center for Global Sea Level Change, NYU Abu Dhabi,Abu Dhabi, UAE
| | - Denis Voytenko
- Courant Institute of Mathematical Sciences, New York University, New York, NY, USA
| | - Knut Christianson
- Department of Earth & Space Sciences, University of Washington, Seattle, WA, USA
| | - Timothy H Dixon
- School of Geosciences, University of South Florida, Tampa, FL, USA
| | - M Jeffrey Mei
- MITWHOI Joint Program in Oceanography, Woods Hole, MA, USA, and Cambridge, MA, USA
| | - Byron R Parizek
- Mathematics & Geoscience, The Pennsylvania State University, DuBois, PA, USA
| | - Irena Vaňková
- Courant Institute of Mathematical Sciences, New York University, New York, NY, USA, and Center for Global Sea Level Change, NYU Abu Dhabi, Abu Dhabi, UAE
| | - Ryan T Walker
- Earth System Science Interdisciplinary Center, University of Maryland, College Park, MD, USA
| | - Jacob I Walter
- Institute for Geophysics, University of Texas at Austin, Austin, TX, USA
| | | | - Denise Holland
- Courant Institute of Mathematical Sciences, New York University, New York, NY, USA, and Center for Global Sea Level Change, NYU Abu Dhabi, Abu Dhabi, UAE
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Murray T, Nettles M, Selmes N, Cathles LM, Burton JC, James TD, Edwards S, Martin I, O'Farrell T, Aspey R, Rutt I, Baugé T. Ice sheets. Reverse glacier motion during iceberg calving and the cause of glacial earthquakes. Science 2015; 349:305-8. [PMID: 26113640 DOI: 10.1126/science.aab0460] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2015] [Accepted: 06/12/2015] [Indexed: 11/02/2022]
Abstract
Nearly half of Greenland's mass loss occurs through iceberg calving, but the physical mechanisms operating during calving are poorly known and in situ observations are sparse. We show that calving at Greenland's Helheim Glacier causes a minutes-long reversal of the glacier's horizontal flow and a downward deflection of its terminus. The reverse motion results from the horizontal force caused by iceberg capsize and acceleration away from the glacier front. The downward motion results from a hydrodynamic pressure drop behind the capsizing berg, which also causes an upward force on the solid Earth. These forces are the source of glacial earthquakes, globally detectable seismic events whose proper interpretation will allow remote sensing of calving processes occurring at increasing numbers of outlet glaciers in Greenland and Antarctica.
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Affiliation(s)
- T Murray
- Glaciology Group, Department of Geography, College of Science, Swansea University, Swansea SA2 8PP, UK
| | - M Nettles
- Lamont-Doherty Earth Observatory, Columbia University, New York, NY 10964, USA
| | - N Selmes
- Glaciology Group, Department of Geography, College of Science, Swansea University, Swansea SA2 8PP, UK
| | - L M Cathles
- Department of Atmospheric, Oceanic and Space Sciences, University of Michigan, Ann Arbor, MI 48109, USA
| | - J C Burton
- Department of Physics, Emory University, Atlanta, GA 30322, USA
| | - T D James
- Glaciology Group, Department of Geography, College of Science, Swansea University, Swansea SA2 8PP, UK
| | - S Edwards
- School of Civil Engineering and Geosciences, Newcastle University, Newcastle upon Tyne NE1 7RU, UK
| | - I Martin
- School of Civil Engineering and Geosciences, Newcastle University, Newcastle upon Tyne NE1 7RU, UK
| | - T O'Farrell
- Department of Electronic and Electrical Engineering, University of Sheffield, Sheffield S1 3JD, UK
| | - R Aspey
- Department of Electronic and Electrical Engineering, University of Sheffield, Sheffield S1 3JD, UK
| | - I Rutt
- Glaciology Group, Department of Geography, College of Science, Swansea University, Swansea SA2 8PP, UK
| | - T Baugé
- Thales UK, Research and Technology, Worton Drive, Reading, Berkshire RG2 0SB, UK
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Murray T, Selmes N, James TD, Edwards S, Martin I, O'Farrell T, Aspey R, Rutt I, Nettles M, Baugé T. Dynamics of glacier calving at the ungrounded margin of Helheim Glacier, southeast Greenland. JOURNAL OF GEOPHYSICAL RESEARCH. EARTH SURFACE 2015; 120:964-982. [PMID: 27570721 PMCID: PMC4981079 DOI: 10.1002/2015jf003531] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/10/2015] [Revised: 04/17/2015] [Accepted: 04/27/2015] [Indexed: 05/25/2023]
Abstract
During summer 2013 we installed a network of 19 GPS nodes at the ungrounded margin of Helheim Glacier in southeast Greenland together with three cameras to study iceberg calving mechanisms. The network collected data at rates up to every 7 s and was designed to be robust to loss of nodes as the glacier calved. Data collection covered 55 days, and many nodes survived in locations right at the glacier front to the time of iceberg calving. The observations included a number of significant calving events, and as a consequence the glacier retreated ~1.5 km. The data provide real-time, high-frequency observations in unprecedented proximity to the calving front. The glacier calved by a process of buoyancy-force-induced crevassing in which the ice downglacier of flexion zones rotates upward because it is out of buoyant equilibrium. Calving then occurs back to the flexion zone. This calving process provides a compelling and complete explanation for the data. Tracking of oblique camera images allows identification and characterisation of the flexion zones and their propagation downglacier. Interpretation of the GPS data and camera data in combination allows us to place constraints on the height of the basal cavity that forms beneath the rotating ice downglacier of the flexion zone before calving. The flexion zones are probably formed by the exploitation of basal crevasses, and theoretical considerations suggest that their propagation is strongly enhanced when the glacier base is deeper than buoyant equilibrium. Thus, this calving mechanism is likely to dominate whenever such geometry occurs and is of increasing importance in Greenland.
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Affiliation(s)
- Tavi Murray
- Glaciology Group, Department of Geography, College of Science Swansea University Swansea UK
| | - Nick Selmes
- Glaciology Group, Department of Geography, College of Science Swansea University Swansea UK
| | - Timothy D James
- Glaciology Group, Department of Geography, College of Science Swansea University Swansea UK
| | - Stuart Edwards
- School of Civil Engineering and Geosciences Newcastle University Newcastle UK
| | - Ian Martin
- School of Civil Engineering and Geosciences Newcastle University Newcastle UK
| | - Timothy O'Farrell
- Department of Electronic and Electrical Engineering University of Sheffield Sheffield UK
| | - Robin Aspey
- Department of Electronic and Electrical Engineering University of Sheffield Sheffield UK
| | - Ian Rutt
- Glaciology Group, Department of Geography, College of Science Swansea University Swansea UK
| | - Meredith Nettles
- Lamont-Doherty Earth Observatory Columbia University New York New York USA
| | - Tim Baugé
- Thales, Research & Technology Berkshire UK
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Moon T, Joughin I, Smith B, van den Broeke MR, van de Berg WJ, Noël B, Usher M. Distinct patterns of seasonal Greenland glacier velocity. GEOPHYSICAL RESEARCH LETTERS 2014; 41:7209-7216. [PMID: 25821275 PMCID: PMC4373171 DOI: 10.1002/2014gl061836] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/18/2014] [Accepted: 10/14/2014] [Indexed: 05/11/2023]
Abstract
UNLABELLED Predicting Greenland Ice Sheet mass loss due to ice dynamics requires a complete understanding of spatiotemporal velocity fluctuations and related control mechanisms. We present a 5 year record of seasonal velocity measurements for 55 marine-terminating glaciers distributed around the ice sheet margin, along with ice-front position and runoff data sets for each glacier. Among glaciers with substantial speed variations, we find three distinct seasonal velocity patterns. One pattern indicates relatively high glacier sensitivity to ice-front position. The other two patterns are more prevalent and appear to be meltwater controlled. These patterns reveal differences in which some subglacial systems likely transition seasonally from inefficient, distributed hydrologic networks to efficient, channelized drainage, while others do not. The difference may be determined by meltwater availability, which in some regions may be influenced by perennial firn aquifers. Our results highlight the need to understand subglacial meltwater availability on an ice sheet-wide scale to predict future dynamic changes. KEY POINTS First multi-region seasonal velocity measurements show regional differencesSeasonal velocity fluctuations on most glaciers appear meltwater controlledSeasonal development of efficient subglacial drainage geographically divided.
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Affiliation(s)
- Twila Moon
- Earth and Space Sciences, University of Washington Seattle, Washington, USA ; Polar Science Center, Applied Physics Lab, University of Washington Seattle, Washington, USA ; National Snow and Ice Data Center, Cooperative Institute for Research in Environmental Sciences, University of Colorado-Boulder Boulder, Colorado, USA
| | - Ian Joughin
- Polar Science Center, Applied Physics Lab, University of Washington Seattle, Washington, USA
| | - Ben Smith
- Polar Science Center, Applied Physics Lab, University of Washington Seattle, Washington, USA
| | | | | | - Brice Noël
- Institute for Marine and Atmospheric Research, Utrecht University Utrecht, Netherlands
| | - Mika Usher
- Polar Science Center, Applied Physics Lab, University of Washington Seattle, Washington, USA
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Bartholomaus TC, Larsen CF, O'Neel S, West ME. Calving seismicity from iceberg-sea surface interactions. ACTA ACUST UNITED AC 2012. [DOI: 10.1029/2012jf002513] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Abstract
The ice sheets of Greenland and Antarctica are losing ice at accelerating rates, much of which is a response to oceanic forcing, especially of the floating ice shelves. Recent observations establish a clear correspondence between the increased delivery of oceanic heat to the ice-sheet margin and increased ice loss. In Antarctica, most of these processes are reasonably well understood but have not been rigorously quantified. In Greenland, an understanding of the processes by which warmer ocean temperatures drive the observed retreat remains elusive. Experiments designed to identify the relevant processes are confounded by the logistical difficulties of instrumenting ice-choked fjords with actively calving glaciers. For both ice sheets, multiple challenges remain before the fully coupled ice-ocean-atmosphere models needed for rigorous sea-level projection are available.
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Affiliation(s)
- Ian Joughin
- Polar Science Center, Applied Physics Laboratory, University of Washington, 1013 NE 40th, Seattle, WA 98105, USA.
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Richardson JP, Waite GP, Pennington WD, Turpening RM, Robinson JM. Icequake locations and discrimination of source and path effects with small aperture arrays, Bering Glacier terminus, AK. ACTA ACUST UNITED AC 2012. [DOI: 10.1029/2012jf002405] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Veitch SA, Nettles M. Spatial and temporal variations in Greenland glacial-earthquake activity, 1993-2010. ACTA ACUST UNITED AC 2012. [DOI: 10.1029/2012jf002412] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Walter F, Amundson JM, O'Neel S, Truffer M, Fahnestock M, Fricker HA. Analysis of low-frequency seismic signals generated during a multiple-iceberg calving event at Jakobshavn Isbrae, Greenland. ACTA ACUST UNITED AC 2012. [DOI: 10.1029/2011jf002132] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Seale A, Christoffersen P, Mugford RI, O'Leary M. Ocean forcing of the Greenland Ice Sheet: Calving fronts and patterns of retreat identified by automatic satellite monitoring of eastern outlet glaciers. ACTA ACUST UNITED AC 2011. [DOI: 10.1029/2010jf001847] [Citation(s) in RCA: 112] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Chen X, Shearer PM, Walter F, Fricker HA. Seventeen Antarctic seismic events detected by global surface waves and a possible link to calving events from satellite images. ACTA ACUST UNITED AC 2011. [DOI: 10.1029/2011jb008262] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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McFadden EM, Howat IM, Joughin I, Smith BE, Ahn Y. Changes in the dynamics of marine terminating outlet glaciers in west Greenland (2000-2009). ACTA ACUST UNITED AC 2011. [DOI: 10.1029/2010jf001757] [Citation(s) in RCA: 71] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Affiliation(s)
- Ellyn M. McFadden
- Byrd Polar Research Center; Ohio State University; Columbus Ohio USA
- School of Earth Sciences; Ohio State University; Columbus Ohio USA
| | - Ian M. Howat
- Byrd Polar Research Center; Ohio State University; Columbus Ohio USA
- School of Earth Sciences; Ohio State University; Columbus Ohio USA
| | - Ian Joughin
- Polar Science Center, Applied Physics Laboratory; University of Washington; Seattle Washington USA
| | - Ben E. Smith
- Polar Science Center, Applied Physics Laboratory; University of Washington; Seattle Washington USA
| | - Yushin Ahn
- Byrd Polar Research Center; Ohio State University; Columbus Ohio USA
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Andersen ML, Larsen TB, Nettles M, Elosegui P, van As D, Hamilton GS, Stearns LA, Davis JL, Ahlstrøm AP, de Juan J, Ekström G, Stenseng L, Khan SA, Forsberg R, Dahl-Jensen D. Spatial and temporal melt variability at Helheim Glacier, East Greenland, and its effect on ice dynamics. ACTA ACUST UNITED AC 2010. [DOI: 10.1029/2010jf001760] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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O'Neel S, Larsen CF, Rupert N, Hansen R. Iceberg calving as a primary source of regional-scale glacier-generated seismicity in the St. Elias Mountains, Alaska. ACTA ACUST UNITED AC 2010. [DOI: 10.1029/2009jf001598] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Murray T, Scharrer K, James TD, Dye SR, Hanna E, Booth AD, Selmes N, Luckman A, Hughes ALC, Cook S, Huybrechts P. Ocean regulation hypothesis for glacier dynamics in southeast Greenland and implications for ice sheet mass changes. ACTA ACUST UNITED AC 2010. [DOI: 10.1029/2009jf001522] [Citation(s) in RCA: 150] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Mugford RI, Dowdeswell JA. Modeling iceberg-rafted sedimentation in high-latitude fjord environments. ACTA ACUST UNITED AC 2010. [DOI: 10.1029/2009jf001564] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Tsai VC, Rice JR. A model for turbulent hydraulic fracture and application to crack propagation at glacier beds. ACTA ACUST UNITED AC 2010. [DOI: 10.1029/2009jf001474] [Citation(s) in RCA: 100] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Amundson JM, Fahnestock M, Truffer M, Brown J, Lüthi MP, Motyka RJ. Ice mélange dynamics and implications for terminus stability, Jakobshavn Isbræ, Greenland. ACTA ACUST UNITED AC 2010. [DOI: 10.1029/2009jf001405] [Citation(s) in RCA: 258] [Impact Index Per Article: 18.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Joughin I, Howat IM, Fahnestock M, Smith B, Krabill W, Alley RB, Stern H, Truffer M. Continued evolution of Jakobshavn Isbrae following its rapid speedup. ACTA ACUST UNITED AC 2008. [DOI: 10.1029/2008jf001023] [Citation(s) in RCA: 182] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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